AC Condenser Cover

We just bought this house in July and the AC system is only a few years old. The previous/original owner is an older guy who actually helped build the house and he is a wealth of information. He told me to never cover up the condenser with plastic, just put a board he made on the top of it and a brick to keep it in place. Our neighbor is a gentleman in his 80's who goes south for the winter and I seen him covering his with plastic before he left. I asked him and he said it is okay to cover it, just leave a gap on the bottom for some airflow.